436 MICRO-ORGANISMS AND DISEASE [chap. 



'• actively immunised " animal is capable of giving im- 

 munity ("passive immunity") to another guinea-pig 

 against the cholera vibrio injected intraperitoneally. There 

 is no difificulty in confirming this discovery of Pfeiffer as 

 to the presence of potential germicidal substances in the 

 blood-serum of an actively immunised guinea-pig. What 

 I have, however, to add, is that according to the above 

 experiments of immunising against living vibrios by means 

 of the intracellular substances only, I conclude that for the 

 production of germicidal serum it is not necessary that 

 there should be produced in the animal body toxins — by 

 the multiplication of the living vibrios injected — for the 

 immunising substances in the above experiments could 

 have been derived solely from the dead bodies of the 

 vibrios used for immunisation. I may state here also that 

 the same evidence I have obtained in showing that 

 germicidal serum of typhoid immunised guinea-pigs against 

 living typhoid bacilli, as also of germicidal serum of 

 diphtheria immunised guinea-pigs against living diphtheria 

 bacilli, is obtainable by using for immunisation the bacillary 

 bodies only, without allowing these microbes to undergo 

 multiplication and production of toxins within the peri- 

 toneal cavity. We shall return to this subject more in 

 detail when treating of immunity. 



Guinea-pigs that by repeated intraperitoneal injections 

 of dead cultures of cholera vibrios have acquired re- 

 sistance by which they can withstand an otherwise fatal 

 dose of living cholera vibrios in their peritoneum, the 

 vibrios not being now able to live and multiply in such a 

 peritoneal cavity, are, however, not proof against cholera 

 toxin. I have made experiments ^ to show that guinea-pigs 



^ Reports of the Medical Officer of the Local Government Board for 

 1S94, 



